This invention relates to power generating steam turbines generally, and, more specifically, to support arrangements for diaphragms within the steam turbine casing.
A typical double-flow, low pressure (LP) steam turbine includes a pair of LP rotor sections surrounded, respectively, by diaphragms, each of which is comprised of a pair of semi-annular diaphragm ring segments that are joined at horizontal joints, spaced 180° from each other. Each ring segment supports a plurality of static nozzles that direct flow into the rotating buckets on axially spaced rotor wheels. The diaphragms are typically located axially between the rows of buckets and are typically supported vertically by any of several known methods. These include support bars, pins or support screws. Each design has its own advantages and disadvantages.
Support bars, for example, currently require that the diaphragm be installed before measurement. After the required measurements are recorded, the diaphragm and rotor are removed so the support bar can be machined to adjust the vertical position of the diaphragm. The sequence is then repeated as necessary to verify the diaphragm position. In addition, current diaphragm adjustment requires removal of both the diaphragm and the rotor as well as bolted-in shims, and can thus take several shifts or days to adjust.
Current support screw designs can only be used on the smaller HP stages because the weight of IP and LP stages is too great. One drawback to the use of support screws is that there is insufficient surface area in the diaphragm cross section to allow for bolting of the upper half diaphragm to the lower half diaphragm. This non-bolted configuration creates a gap between the half-sections at the horizontal split or joint line, causing turbine efficiency losses.
Support pins are generally used in LP turbines, but they cannot support as much weight as support bar designs.
Accordingly, there remains a need for an easily accessible support arrangement that facilitates vertical adjustment of the diaphragm ring segment in a relatively quick and efficient manner.